1. Field of the Invention
The present invention relates to a plastic optical fiber with a lens in which the lens having a light-condensing function or the like is integrally attached to the end face of the optical fiber, a light-emitting/receiving apparatus (this term means a light-emitting apparatus or a light-receiving apparatus in this specification) in which a light-emitting/receiving device (this term means a light-emitting device (such as a laser diode) or a light-receiving device (such as a photodiode) in this specification) is combined with the plastic optical fiber with a lens, and a method of fabricating the plastic optical fiber with a lens.
2. Related Background Art
Conventionally, in order to enhance the coupling efficiency between plastic optical fibers, or a plastic optical fiber and a light-emitting device/receiving device, there have been proposed some methods of forming a convex lens at the end face of the plastic optical fiber. For example, Japanese Patent Application Laid-Open No. 10 (1998)-239538 discloses a method of forming a spherical convex contour on the end face of a plastic optical fiber by using a solvent, Japanese Patent Application Laid-Open No. 11 (1999)-326689 discloses a method of forming a spherical convex contour on the end face of a plastic optical fiber by immersing the end thereof in an organic solvent containing an optical fiber material and drying this end face after the optical fiber is lifted from the solvent, Japanese Patent Application Laid-Open No. 5 (1993)-107427 discloses a method of forming a spherical convex contour on the end face of an optical fiber by immersing the end thereof in a photosensitive resin and hardening this end face after the optical fiber is lifted from the resin, Japanese Patent Application Laid-Open No. 8 (1996)-75935 discloses a method of forming a lens shape on the end face of an optical fiber by pressing the end face thereof on a heated lens forming mold, and Japanese Patent Publication No. 62 (1987)-57001 discloses a method of forming a spherical convex surface on the end face of an optical fiber by heating and softening this end face, using surface tension.
Further, there have been proposed, as an art of fabricating a concave contour on the end face of a plastic optical fiber with a refractive index distribution, a method of molding the end face of an optical fiber by a heated metal mold, and a method of forming a concave contour on the end face of an optical fiber by applying a solvent (see Japanese Patent Application Laid-Open No. 11 (1999)-242129).
In those conventional methods, however, precision in centering a light-condensing axis of the spherical convex surface is not sufficiently satisfactory, and alignment between the light-emitting/receiving device and the optical fiber needs to be additionally conducted after the optical fiber is fabricated. Moreover, since the end face of the optical fiber has a spherical convex contour, tolerance of its positional deviation is small, compared to an optical fiber with a flat end face.
It is an object of the present invention to provide a plastic optical fiber with a lens, in which the lens having a light-condensing function or the like is integrally attached to an end face of the optical fiber and which has an excellent reproducibility, its fabrication method, a light-emitting/receiving apparatus in which a light-emitting/receiving device is combined with the plastic optical fiber with a lens, and its fabrication method. The plastic optical fiber refers to an optical fiber whose core and cladding are made of polymer, and an optical fiber whose core is made of polymer. In such a plastic optical fiber, the cladding may be covered with a protective layer, or a polymer jacket. Further, the plastic optical fiber may be a step-index (SI) type wherein a refractive index along its radial direction is uniform throughout but exhibits an abrupt step at its core-cladding interface, a graded-index (GI) type wherein a refractive index varies in some continuous fashion as a function of radial distance, or the like.
The present invention is generally directed to a plastic optical fiber with a lens, which includes a plastic optical fiber having a core and a cladding, and a lens having a function of controlling light rays. The lens is formed of a material with a thermally-softening temperature higher than a thermally-softening temperature of the core of the plastic optical fiber, and the lens is integrated with the plastic optical fiber by heating and pressing the lens against an end face of the plastic optical fiber.
In the plastic optical fiber with a lens of the present invention, the lens is heated to a temperature below the thermally-softening temperature of the lens and above the thermally-softening temperature of the core of the plastic optical fiber, and the end face of the plastic optical fiber is molded and integrated with the lens by using the heated lens as a mold. The end face of the plastic optical fiber is preferably cut by a cutter and shaped into a flat surface. Further, after the end face of the plastic optical fiber is molded and integrated with the lens, it is preferable to surely bond the lens to the plastic optical fiber with an adhesive.
On the basis of the above structure, the following more specific structures are possible.
Any lens can be used as far as the lens has a function of controlling light rays. Typically, the lens is a light-condensing lens with a spherical surface (e.g., a ball lens), or a light-condensing lens with a semispherical surface. The semispherical lens can be typically attached to the end face of the optical fiber by pressing the semispherical face against the end face of the optical fiber. In this case, an outer face of the optical fiber with the semispherical lens becomes flat, and therefore, the optical fiber can be readily handled. Other lenses, such as a cylindrical graded-index lens, a convex or concave meniscus lens, and an aspherical lens, can be used according to applications.
The lens is typically formed of glass or resin whose thermally-softening temperature is relatively high. The plastic optical fiber is typically a totally-fluorine-contained plastic optical fiber or the like.
It is preferable that the lens have a diameter smaller than a diameter of the plastic optical fiber, and be bonded to the plastic optical fiber at its peripheral portion with an adhesive.
Further, the present invention is generally directed to a method of fabricating a plastic optical fiber with a lens, which includes a step of preparing a thermally-conductive substrate for holding a lens in a predetermined position, a step of heating the substrate and the lens held thereby to a temperature below a thermally-softening temperature of the lens and above a thermally-softening temperature of a core of a plastic optical fiber, and a step of pressing an end face of the plastic optical fiber against the heated lens and molding the end face of the plastic optical fiber to integrate the lens with the plastic optical fiber and cause an end of the plastic optical fiber to have a function of controlling light rays (e.g., a light-condensing function).
On the basis of the above method, the following more specific methods are possible.
A portion with a contour for holding the lens in the predetermined position can be formed directly (see an example of FIG. 6) or indirectly (see an example of FIG. 1) on the thermally-conductive substrate.
An adjusting surface for adjusting a positional relationship in an optical-axial direction between the lens and the plastic optical fiber can also be formed near the portion with a contour for holding the lens, and a periphery of the end face of the plastic optical fiber can be caused to abut the adjusting surface when the end face of the plastic optical fiber is pressed against the heated lens.
An alignment member for holding an end portion of the plastic optical fiber and aligning optical axes of the lens and the plastic optical fiber with each other can be provided on the substrate, and the optical axes of the lens and the plastic optical fiber can be caused to align with each other when the end face of the plastic optical fiber is pressed against the heated lens.
Furthermore, the present invention is generally directed to a light-emitting/receiving apparatus which includes a light-emitting/receiving device arranged on a substrate, and the above-discussed plastic optical fiber with a lens of the present invention. The lens is held above the light-emitting/receiving device.
On the basis of the above structure, the following more specific structures are possible.
The lens can have a diameter smaller than a diameter of the plastic optical fiber, the portion for holding the lens can be a recess whose size is larger than the diameter of the lens and smaller than the diameter of the plastic optical fiber, and the adjusting surface can be a surface around the recess.
The portion for holding the lens can be formed integrally with and of a material common to the lens (see an example of FIG. 8).
An alignment member for holding an end portion of the plastic optical fiber and aligning optical axes of the lens and the plastic optical fiber with each other can be provided on the substrate. In this case, the plastic optical fiber can be bonded to the alignment member with an adhesive at its periphery.
Furthermore, the present invention is generally directed to a method of fabricating a light-emitting/receiving apparatus, which includes a step of preparing a thermally-conductive substrate for arranging a light-emitting/receiving device and holding a lens in predetermined positions, respectively, a step of arranging the light-emitting/receiving device in the predetermined position on the substrate, a step of holding the lens in the predetermined position on the substrate, a step of heating the substrate and the lens held thereby to a temperature below a thermally-softening temperature of the lens and above a thermally-softening temperature of a core of a plastic optical fiber, and a step of pressing an end face of the plastic optical fiber against the heated lens and molding the end face of the plastic optical fiber to integrate the lens with the plastic optical fiber and cause an end of the plastic optical fiber to have a function of controlling light rays.
In the method of fabricating the light-emitting/receiving apparatus, the lens is appropriately positioned above the a light-emitting/receiving device arranged on the substrate. Thereafter, the lens is heated to the above temperature, and the end face of the plastic optical fiber is pressed against the heated lens and molded thereby to integrate the lens with the plastic optical fiber. Finally, the plastic optical fiber may be assuredly fixed to the lens with an adhesive or the like. This method is substantially the same as the above-discussed method of fabricating a plastic optical fiber with a lens of this invention.
Here, the position of the lens above the light-emitting/receiving device and alignment between the lens and the plastic optical fiber in integrating the plastic optical fiber with the lens are important. For example, when the diameter of the lens is smaller than that of the plastic optical fiber, a layer with a recess of a size larger than the lens and smaller than the optical fiber is provided on the substrate to align the light-emitting/receiving device with the lens and adjust the distance in an optical-axial direction between the lens and the optical fiber. Further, a layer for holding the optical fiber and aligning the optical fiber with the lens and the light-emitting/receiving device may be formed on the layer with a recess in order to achieve all-directional alignment between light-emitting/receiving device, lens and plastic optical fiber.
These and other advantages will be more readily understood in connection with the following detailed description of the more preferred embodiments in conjunction with the drawings.